Conventionally, regarding electric energy storage devices like a lithium ion secondary battery, reduction in size and in weight, thinning and a degree of freedom of shape become highly requisite in accordance with expansion of its various applications.
In response to such requisites, there is proposed a sheet-like lithium ion secondary battery which is lightweight, thin, and flexible and which has a flexible outer package body as a battery case comprising a multilayered laminated film including an internal layer formed of a thermoplastic resin with good electrolysis-solution tolerability and heat seal characteristics, such as polyethylene or polypropylene, a middle layer formed of a metal foil with good flexibility and strength like an aluminum foil, and an external layer formed of an insulating resin with a good electrical insulation property like polyamide, and wherein a sheet-like internal electrode pair and an electrolysis solution are filled in the outer package body (see, for example, patent literatures 1 and 2).
Patent literature 1 discloses a sheet-like secondary battery comprising an internal electrode pair including a sheet-like positive electrode, a separator, and a sheet-like negative electrode all stacked together, an outer package body retaining the internal electrode pair thereinside, an internal lead connected to the internal electrode pair, an external lead sandwiching the outer package body and arranged outwardly thereof, and connection means for electrically connecting the internal lead and the external lead together by airtightly passing all the way through the outer package body, and the outer package body is firmly and airtightly held between the internal lead and the external lead to improve the sealing property and the connection reliability.
Patent literature 2 discloses a secondary battery comprising an electrode body with a protrusion, and an outer package body covering and wrapping the electrode body, the protrusion passes all the way through the outer package body and protrudes to the exterior of the battery, a sealing member is provided around the protrusion, and an insulating material is provided at a portion where the protrusion contacts the outer package body. More specifically, after a protrusion 41 is allowed to protrude from an outer package film 3, a sealing member 5 which seals a space between the protrusion and the outer package film is provided around the entire periphery of the protrusion 41, thereby suppressing any short-circuiting as the protrusion 41 contacts a metal foil of the outer package film 3 when the protrusion 41 of an external terminal 4 passes all the way through the outer package film 3    Patent Literature 1: JP2003-151529A    Patent Literature 2: JP2003-331819A